Plasma etched polymer microelectrochemical systems Joël S. Rossier,* a Christine Vollet, a Amanda Carnal, b Grégoire Lagger, b Véronique Gobry, b Hubert H. Girault, b Philippe Michel a and Frédéric Reymond a a DiagnoSwiss, Rte de l’Ile-aux-Bois, c/o Cimo S.A, 1870 Monthey, Switzerland b Laboratoire d’Electrochimie, Ecole Polytechnique Fédérale de Lausanne, Laboratoire d’Electrochimie Physique et Analytique, 1015 Lausanne, Switzerland Received 26th April 2002, Accepted 2nd July 2002 First published as an Advance Article on the web 17th July 2002 This paper presents a novel technique based on plasma etching for the mass production of polymer microchip devices. The method consists of the patterning of a photo-resist by a high resolution printer on a foil composed of three layers (5 mm copper/50 mm polyimide/5 mm copper). After this step, both copper layers are chemically etched in order to serve as a contact mask on the polyimide surface so as to produce the desired microstructure pattern. The foil is placed into a reactive plasma chamber in order to etch the exposed polyimide by means of an oxidizing plasma. The method enables holes, lines or larger areas to be etched, thereby generating either microholes, microchannels or electrodes in the plastic material. The copper can then be chemically removed or further patterned to produce conductive pads which are further electroplated with gold. The microchannel is then covered with a polyethylene terephthalate/polyethylene (PET/PE) lamination. The strength of this technology is that access holes for the fluid inlet and outlet, as well as gold coated electrodes can be fabricated without post-processing in a batch process. Demonstration of the application of such microelectrochemical systems is shown here by voltammetric detection inside a 60 nL microchannel, which presents the special feature of linear depletion of the analytes in the direction parallel to the microchannel. Introduction One of the current trends in analytical chemistry is the miniaturisation of instruments to small microchips actuated by electrical means. The development of these microelectro- mechanical systems (MEMS), also known as miniaturised total analytical systems (m-TAS), has principally been applied in the genomic area but has also been developed for proteomic applications. 1 Numerous authors have presented the separation of DNA strains by capillary electrophoresis with fluorescence detection . The success of this application, sometimes combined with PCR 2 on a chip, has promoted the interest in m-TAS. Novel applications of the concept in various fields such as protein analyses and combinatorial chemistry are under development. Other areas such as analytical sensors have also benefited from the availability of this technology to present even more integrated analysers with a shorter response time. 3 Never- theless, in order for these applications to be successful they need to meet high quality and mass production capacities in order to be affordable in the competitive world of the analytics and, more precisely, in the diagnostics area. 4 One possible way of enabling the transfer of this technology from the early stage silicon or glass prototypes to low cost m- TAS is the fabrication of microchips in polymer substrates. 5 Polymer microstructures can be produced nowadays in high volumes using simple technologies such as hot embossing, injection moulding or polydimethylsiloxane (PDMS) casting. These technologies facilitate the use of sealing procedures such as thermal bonding, 6 lamination 7 or plasma bonding 8 thereby enabling efficient bonding with a high yield, which still remains problematic with glass or silicon fabrication. If a decrease in cost can be achieved, it is expected that these technologies will enable single use applications in medical diagnostics, thereby reducing the risks of cross-contamination during sequential analyses. For some applications in sensor technology, it is necessary to integrate microelectrodes inside microstructures in order to use them as electrochemical detectors 9 or to apply the spray voltage in mass spectrometry coupling processes. 10,11 It has previously been shown that microelectrodes enable detection in pico- liter 12,13 to nanoliter volumes. 14,15 Some ways of addressing the integration of electrodes have been previously shown in polymer channels made by means of laser photoablation, 9 embossing 16 or PDMS casting. 17,18 Integrated electrodes have been used in enzyme-linked-immunsorbent-assays (ELISA) 19,20 or capillary electrophoresis with electrochemical detection 17,21 as well as in the fabrication of plastic nano- electrosprays. 10,11 Although laser photoablation and PDMS fabrication are interesting prototyping tools, mass production with the actual technologies still seems to be difficult. This report presents a new fabrication principle based on plasma etching that allows high volume fabrication. This technology has been used since 1992 in the electronics industry for the fabrication of very compact printed circuit boards. It has already been applied in the production of polyimide-based high- density interconnects (HDIs) and multi-chip-modules (MCMs) for avionics, pace-makers, hearing-aid devices and even in satellites. This plasma-based interconnect technology has proven its robustness in a broad range of applications, and it has been recently adapted to the manufacture of microfluidic devices. 20,22 The concept of this technology, developed by Dyconex (Switzerland), and known under the trademark DYCOstrate® can be characterized simply by the substitution of the mechanical drilling, laser ablation or wet etching in glass by plasma ablation in thin dielectrics, such as polyimide or almost any other organic material. This paper presents the plasma etching fabrication technol- ogy and the voltammetric detection obtained within 60 nL microchannels, where working, counter and reference elec- trodes are integrated. These microstructures are used here to study the particular diffusion behaviour of electroactive species in the microchannel following previously described experi- ments, 9 where calculation showed that microelectrodes behave differently from their standard behaviour in microchannels. This journal is © The Royal Society of Chemistry 2002 DOI: 10.1039/b204063h Lab Chip, 2002, 2, 145–150 145 Published on 17 July 2002. Downloaded by ECOLE POLYTECHNIC FED DE LAUSANNE on 24/10/2013 09:55:47. View Article Online / Journal Homepage / Table of Contents for this issue